Method onMessage

src/service/viewer-impl.js:659–674

@override

(eventType, handler)

  /** @override */
  onMessage(eventType, handler) {
    let observable = this.messageObservables_[eventType];
    if (!observable) {
      observable = new Observable();
      this.messageObservables_[eventType] = observable;
    }
    const unlistenFn = observable.add(handler);
    if (this.receivedMessageQueue_[eventType]) {
      this.receivedMessageQueue_[eventType].forEach((message) => {
        observable.fire(message.data);
        message.deferred.resolve();
      });
      this.receivedMessageQueue_[eventType] = [];
    }
    return unlistenFn;
  }

  /** @override */
  onMessageRespond(eventType, responder) {